Thermomechanical coupling effects on mechanical behavior and deformation mechanism of Al0.2CoCrFeNi high-entropy alloy under extreme conditions

High-entropy alloys exhibit significant potential for applications in extreme environments, particularly under high temperature and high strain-rate coupled loading conditions relevant to aerospace components. However, research on their mechanical properties under such coupled extreme conditions remains limited. Compressive behavior of the Al0.2CoCrFeNi HEA over a wide range of temperatures and strain rates was studied, using an improved Hopkinson pressure bar system and an electronic universal testing machine. The results demonstrate significant temperature and strain rate dependence of the flow behavior within the selected temperature and strain rate ranges. Third-type strain aging phenomenon, characterized by an anomalous flow stress peak within a specific temperature range and accompanied by Portevin-Le Chatelier serrated plastic flow, was observed under quasistatic condition and disappeared under high strain-rate conditions. The solute atomic in situ pinning mechanism dominated by Al atoms is comprehensively elucidated to further understanding of third-type strain aging phenomena in HEAs. Microstructural evolution at different temperatures and strain rates was characterized. Multiple deformation mechanisms, including twinning, dislocation slip, and dynamic recrystallization, were systematically investigated to elucidate their evolution with temperatures and strain rates. Finally, a deformation mechanism map was proposed over a wide temperature and strain rate range. This work provides fundamental insights into optimizing the strength-ductility synergy of HEAs for extreme environment applications, and the proposed deformation mechanism map offers guidance for the composition design and microstructure optimization of HEAs.